Method and apparatus for determining characteristics of earth formations



JNVEN R. GI Dun hole GLANVILLE ET AL T D AND APPARATUS FOR DETERMIN GCTERI STICS Filed Ma ME C Charles Henry F. Ellis W. S

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TORS onville Io p ATTORNEY Patented July 14, 1953 "2345752 j V METHODAND APPARA S mmals me CHARACTERISTICS, OF EARTH, roa

MATIONS Gharle's R. Glanville,'llenry F. Di'inla'p, ahd 'Ellis W.shuler, In, Dallas, Tex assigno'rs to "The f A'tIaLntic-ReIiningCompany,BhiladelphIm'Pm, acorporation Pennsylvania. a I

AppllcationTMarchi), 1951', sm rt-7214msummon (cheat-am This inventionreiaites to method and "apparatus for determining permeability andfo'rm'w tion resistance factor of earth formations, and

particularly to method and apparatus "for making such determinationsfrom rel'ajtively "small cuttings taken '"from 'su'c'h formations. V I IIn order to determine whether or not hydrocarbons are present in earthformations, and also "to determine the ease with whiohohy hydrocarbonswhich are present may berernoved it is necessarythatcertaincharacteristics of the formation "be measured. Among thesecharacteristios is that o'f 'f'o'rmation resistance factor."

The formation resistance factor, a-s'is well l'gn'own in the art, istheratio or the resistivity of a sample of the formation which is 100%saturated With a brine solution to the resistivity or course'mtcommanders brought to'th'e surface broken noose trom fonnation intheordinary oftheearthwith "thereturnin drilling fluid. I It is anotherobject; of this invention to'provid'e afi'nthod wliereby cuttings from aformation 1 may be mounted itrahon-porous; non-conduct the saturatingbrine. By correlation of the fo'r-' mation resistance factor withcertain electrical measurements made on the formation in its nativestate, an estimate can be made "as-to the likelihood of the presence ofhydrocarbons in the formation. H

Hereto'fore formation resistance factor has been o'btained'by makingthenece's'sary measurements upon core samples obtainei i from "therorm'ation undergoing test by means of 4a spo'cioi core drilling tool.Thereare undeniamo aovantag'es to workin with core samples of relat velylarge and uniform size, 'but the obtaining of such samples is anexpensive, and often dii-ilcul't,

undertaking. The securing of a core sample.

always necessitates removal of the tool string and replacement of thedrilling bit with a special core bit, running the core bit into the holet'o secure a sample, withdrawing it, and "resisting I the drill bitprior to continuing the drilling operation. It will be seen -that suchan operation is an expensive and time consuming one,"par'- ticularly inthe case of the investi ation or forma'tions several thousands of: 'feetbelow the ear'ths surface. Inadd'ition't'o the fact that the securing of"core samples is always aidi'fficult task at best it frequently occursthat, due to the'na ture of the formation undergoing examination, it isimpossible to obtain asuitable core sample. According-I37, it is 0f1e'bbj'ect of this invention to provide method and ap aratus whereby theresistance factor of a formation may be deter mined without thenecessity of obtainingcore' samples from the formation.

It is another object of this invention to pro vide "method and apparatuswhereby -"furination resistance factor determinations may be made; fromcuttings of a formation; which cuttin s are ingniateria'n'order'to-i'acilitate the making of formation resistance factordeterminations. Other'objefcts' and advantages of this invention willbecome apparent from the following detailed*doscriptiontaken inconnection with theappeiid'eddrawings;

F igure l isa perspective view of a disk, used in aoc'ord-aihce' withthe teachings 'ofthis inven two, which comprises cuttings from afo'rmation i'mb'edded in 'a fiuid4mpervi'ous, electrically-insu- 1atmgsiippoi tin'gmaterial'. jFigure 2 is an elevation, partially in section,of an apparatus designed roruse'in making formation resistance ffactordeterminations in accordance'withthe methodof'this invention.

* riefly, "this invention relates "to "method and apparatus whereby'formation resistance factordeterininati'ons maybe 'm'a'de where, forone reas'o'n oranother, only ordinary drill cuttings or other smallfragments o'f'the formation are available, although the invention mayalso "be ractic'e'd, if'de'sired; wherecores are obtainable.

Accordingto this invention, cuttings or other smallfragin'entsof theformation :are imbedded,

or "bonded, in" a -iiias's of fluid-impervious,el'ectridaily-insulating,supporting material. The body thus forlned or:the cuttings and supporting mate'ii'alf'i's then sliaped into a water ofany desired size and shape, and material removed from the is thenmounted in a suitable holder'and a currentoi electricity passedtherethrough While the voltage drop thereacro ss is measured. Since thesupporting material is a non-conductor of "electricityfthevoltage dropacross the wafer serves as ameasuro 'of -tl'ie' 'resistance of thecuttings. This data, plus a knowledge of cutting "dimensions and br-ineresistivity; will permit formation resistance ractor of' the cuttings tobe calculatefli" Y the'fii awings Figure :l' shows 'a wafer,preferablyflisk shapedfigenerally designated :by the numeral I, which iscomposed of one or more cuttings 2 imbedded in a body 3 offluid-impervious, electrically-insulating, and preferably transparentmaterial. Materials which have been found to perform satisfactorily forthis purpose are methyl methacrylate, more commonly referred to by thetrade name Lucite,

carbon solvent and any moisture which might be 1 present in the pores ofthe samples. After cleaning, the edges and at least one face of the moreirregular cuttings are sanded so that the edges will be substantiallyperpendicular to the face. The cuttings having thus been cleaned andsanded are ready to be'mounted in the support-- ing material. V

For this purpose a mold, not shown, of any desired size or shape, butpreferably circular and of a diameter of one inch, may be used. A smallamount of Lucite powder, preferably enough to form a wafer about 1 3'"thick, is placed in the bottom of the mold and subjected to a pressureof 1,000 p. s. i. and a temperature of 210 F. for a suflicient time(approximately one-half to one minute) to cause it to become partiallypolymerized. Thereafter, one or more of the previously prepared cuttings2 are placed on the partially polymerized wafer in such manner that theedges of the several cuttings will be substantially perpendicular to theface of the wafer. The cuttings are then covered with Lucite powder to adepth of about above their upper faces. The contents of the mold arethen subjected to a pressure of 1,000 p. s. i. and a temperature of 275F. for approximately three to five minutes to thus form a wafer aboutthick consisting of the cuttings completely molded and encased in afully polymerized Lucite body.

The faces of the wafer are then sanded, preferably with a heavysandpaper until the full faces of all cuttings are exposed on each sideof the wafer. Thereafter a fine sandpaper may be used to polish bothfaces of the wafer. Care should be taken that the wafer is not sanded sothin as to be excessively fragile and hence likely to break duringsubsequent handling. In the case of a wafer 1" in diameter it has beenfound that the wafer should not be sanded to a thickness of less thanabout .05 cm.

After completing the mounting, the cuttings mounted in the wafer arewashed to remove foreign matter and then saturated with brine by meanswell known to those skilled in the art.

By using apparatus shown in Figure 2 a wafer, or disk, as describedabove and shown in Figure 1 may be employed for making formationresistance factor determinations. In this drawing, a wafer I is shownclamped in a cell 4 having upper and lower body sections 5 and 6,respectively, which are clamped together by any suitable means such asthreaded connector ring I. Body sections 5 and 6 are made of anelectrically insulating material, such as Lucite. Wafer I rests on aninternal annular shoulder 8 provided at the upper end of the innerperiphery of lower body section 6. A sealing ring 9 made of any suitablenon-conducting resilient material, such as rubber, is located atop waferI and in contact with the outer edge thereof so as to form a sealtherewith. The upper edge of resilient ring 9 makes sealing contact withannular shoulder I0 provided at the lower edge of the inner periphery ofupper body section 5.

Prior to placing wafer I in cell 4, the cuttings 2 imbedded therein aresaturated with brine by any process known to those skilled in the art.In assembling wafer I in cell 4, both upper and lower sections 5 and 6are filled with a brine like that used to saturate the cuttings 2. Theseal between wafer I, shoulders 8 and I0, and resilient ring 9 preventsthe escape of brine from cell 4. The'upper end of upper section 5 isprovided with an opening'I I through which a thermometer IZ-may beinserted for the purpose of observing temperature of 'the brine incompartment 5. Any suitable means may be utilized to support thethermometer I2, as for instance rubber stopper I3; Disks I4.and I5 of anelectrically conducting materialare secured in the upper end of uppersection 5 and. the lower end of section 6, respectively, disk I4 beingprovided with an opening to permit thermometer I2 to pass therethrough.Screw contactsIB and I I are employed to provide a path for electricity,through the walls of cell 4 to the exterior thereof, from disks I4 andI5 respectively. Ring I8, also of conducting material, is located incompartment 5 intermediate the ends thereof, and conducting ring I9 islocated in compartment 6 intermediate its ends. Screw contacts 20 and 2|serve as external contacts for rings I8 and I9, respectively.

In operation, a measured current is passed through cell 4 betweencontacts I6 and I1, while the voltagedrop between contacts 20 and II ismeasured. The temperature within cell 4, as indicated by thermometer I2,is observed atthe same time. After correction for the resistance of thebrine between rings I8 and I9 on opposite sides of wafer I,the voltagedrop between contacts 20 and M serves as an indication of the resistanceof the brine-saturated cuttings 2, which may be used together with thetemperature reading and the dimensions of cuttings 2 to determine theformation resistance factor of the formation from which the cuttingswere taken. by calculations known to those skilled in the art.

While the method of measuring the thickness and cross-sectional area ofthe cuttings 2 included in any disc I forms no part of the presentinvention, it is suggested that the thickness be measured by means of anordinary micrometer caliper. The cross-sectional area may be mostaccurately determined by making an enlargement of the disc by anysuitable means, such as photographically, and measuring the area of thecuttings by means of a planimeter. Alternatively. this cross-sectionalarea of the cuttings may be measured photoeleotrically by comparing theamount'of light transmitted through a disc I carrying cuttings 2 to thelight transmitted through a disc of similar material in which there areno cuttings, the amount of light transmitted being a function of theportion of the path obstructed. The difference in light transmitted by aclear disk and one having cuttings in it serves as a measure of theproportion of the light path obstructed by the cuttings and hence as ameasure of the cross-sectional area of said cuttings.

While theabove specification and drawings describe preferred method andapparatus for carrying out this invention, it will be appreciated bythose skilled in the art that numerous minor modifications may be madewithout departing from the spirit and scope thereof;

We claim:

1. A wafer for use in measuring the characteristics of an earthformation which comprises a cutting from said earth formation and a massof fluid-impervious, electrically-insulating material surrounding saidcutting, the upper and lower faces of said cutting being flush with theupper and lower surfaces respectively of said mass.

2. A wafer for use in measuring the characteristics of an earthformation which comprises cuttings from said earth formation and a massof fluid-impervious, electrically-insulating material laterallysurrounding said cuttings, the upper and lower faces of each of saidcuttings being fiush with the upper and lower surfaces respectively ofsaid material and the edges of said cuttings being substantiallyperpendicular to said faces.

3. A method of determining the resistance factor of a formationcomprising the steps of obtaining cuttings from the formation, forming acylinder of fluid-impervious, electrically insulating material aroundsaid cuttings in such manner as to form a substantially fluid-tight bondbetween said cuttings and said material, removing material from the endsof said cylinder to expose a face of each of said cuttings at each endof said cylinder, saturating said cuttings with brine solution, andmeasuring the resistance to flow of electric current through saidcylinder.

4. A method for determining the resistance of an earth formationcomprising the steps of obtaining cuttings from the earth formation,embedding said cuttings in a mass of fluid-impervious,electrically-insulating material to form a Wafer in which said cuttingsare bonded with said mass with only opposite parallel faces of saidcuttings exposed on opposite sides,- respectively, of said wafer,saturating the cuttings with an electrolyte,passing an electric currentthrough the cuttings, and measuring the voltage drop thereacross.

5. A method for determining the resistance factor of an earth formationcomprising the steps of obtaining cuttings from the earth formation,embedding said cuttings in a Wafer of fluid-impervious,electrically-insulating material, exposing the surfaces of each of saidcuttings at opposite faces, respectively, of said wafer, saturating thecuttings with an electrolyte, passing an electric current through thecuttings, and measuring the voltage drop thereacross.

CHARLES R. GLANVILLE. HENRY F. DUNLAP.

ELLIS W. SHULER, JR.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 882,265 Neall Mar. 17, 1908 1,509,495 lSlepian Sept. 23, 19241,545,186 Henriksen et a1. July 7, 1925 1,856,680 Williams et al May 3,1932 2,460,534 Richards Feb. 1, 1949

